Ewing's sarcoma gene (EWS) belongs to a family of TET proteins, which include TLS/FUS and TAFII15. These proteins encode RNA binding domain at the C-terminal end and a large repeats of SYGOO motif at their N-terminus. Based on the physical interactions with RNA polymerase II and splicing factors, TET proteins are thought to play roles in basic transcription and splicing. However, in vivo role of EWS and other TET proteins has not been demonstrated. Thus, the goal of this project is to understand the in vivo function of EWS and to relate that function in the context of the chromosomal translocation found in Ewing's sarcoma and other EWS-fusion sarcomas. Aim 1. We will generate EWS knockout mouse by gene targeting approach. We have already generated the knockout mouse derived from the targeted mouse ES cells. Aim 2. To characterize the defects caused by EWS deficiency in the knockout mouse. Aim 3. To characterize the EWS deficiency at the cellular level to identify the mechanisms by which EWS functions. The knowledge gained from this study will help to better understand about EWS and other TET proteins in general. This will further elucidate how EWS or TLS related fusion products will lead to tumorigenesis.